fix: reject invalid EasyEDA component detail responses

[alexci04]

The component-details request currently checks HTTP status but ignores the JSON success flag. A response with success: false can return geometry as if it succeeded; a missing result returns undefined when model metadata is disabled or produces a TypeError when enabled.

This adds component-envelope validation before model metadata lookup, preserving the raw geometry for the existing conversion layer. Failures identify the requested part and include the API error code/message when available. The change follows the existing search-response validation pattern.

Validation:

• 18 initial offline regression cases failed on unmodified main (06077ed); expanded coverage now includes missing/empty UUIDs.
• 39 focused fetch tests pass, including 22 new cases covering both metadata settings, existing exact-match behavior, search errors and HTTP rate limiting.
• TypeScript --noEmit, formatting for the three changed files, git diff --check, and the library/browser/CLI build pass.
• Checked one public component-details response to confirm the success/code/result envelope. The malformed responses are injected regression cases, not a claim of a live API outage.
• Full image/network test suite not run.

Prepared and tested with OpenAI Codex assistance. No fixed bounty or payment is claimed for this contribution.